The present invention relates to a method and apparatus for positioning a femoral stem hip prosthesis in a femoral canal with the use of a cement.
It is well known in the prior art to initiate total hip replacement as disclosed in U.S. Pat. Nos. 4,357,716, granted Nov. 9, 1982, and 4,718,909, granted Jan. 12, 1988. As described in these patents, the femur is prepared to receive a femoral stem prosthesis which has a head, neck and stem. The proximal end of the femur is prepared by resecting the head and neck of the femur and then reaming and possibly rasping or curetting the intramedullary canal. Once the canal has been properly prepared by reaming and curettage, the distal canal is plugged, utilizing a bone plug obtained from the femoral head or formed in any other of the well known alternate methods. In any event, the plug effectively seals off the canal to prevent excessive penetration of cement below the tip of the stem of the prosthesis. Positioning of the prosthesis stem in the femoral canal and the relationship of the head and neck of the prosthesis with the shaft of the femur is important and is related in part to the position of the distal end of the femoral stem as well as the position of the proximal end of the prosthesis stem in the intertrochanteric area.
As described in U.S. Pat. No. 4,357,716, a fixed device or apparatus holds the prosthesis in fixed relationship to the femur thus eliminating motion of the prosthesis during the time that the pressurized cement is applied about the prosthesis stem in the femoral canal, and the pressure is maintained until the cement hardens.
The proposals of the above-identified patent have been efficacious in contributing to the successful implantation of prostheses in which the stems and heads are formed integrally. However, there have more recently been proposed prostheses in which the heads can be and in fact are separated from the remainder of the prostheses. Such separation feature makes it possible for the stem of a prosthesis to be handled more easily than if the head were permanently attached and it also makes possible the mounting of heads to optimally fit the prosthesis to the particular characteristics of the patient.
As is known to those skilled in the art, the heads of hip replacement prostheses must be machined to extraordinarily high tolerances and finely polished so as to provide surfaces adapted for relative movement as is occasioned when a patient walks after the prosthesis has been installed and healing has occurred. Even the slightest nick on such a highly machined head can render the entire device inoperative and it must then be discarded. Since prostheses are relatively expensive, it will be evident that the removability of the head constitutes a significant improvement, at least in some instances; and, consequently, prostheses having removable heads have become increasingly attractive.
As described with respect to the above-identified patents, a feature of the previously proposed apparatus or devices made use of the neck of the prosthesis (the portion adjacent to the head) for the purpose of holding the proximal end of the prosthesis in position while cementing was occurring. However, with the removable head feature, most necks are no longer suitable for this purpose. Moreover, according to the prior art proposals, utilization of the neck portion of the prosthesis for holding resulted in a relatively small degree of adjustability, thereby in some instances unduly restricting the adjustment needed by the surgeon. In addition, when a stem prosthesis with a removable head is implanted, there continues to be a need to protect the finely machined neck. Accordingly, there has continued to be a need for an improved versatile device or apparatus which is adapted for use with both removable and fixed head prostheses.